Mk3 jetta and passat tdi yearly differences and interchangeable parts
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Introduction 

The VW TDI was introduced to the US in 1996.  There was a turbocharged ecodiesel available in Canada but there are some big differences between the ecodiesel and TDI.  The ecodiesel has less performance, no intercooler, a cold start assist handle on the dashboard, and the glow plugs were activated by opening the driver's side door.  It also had the old style cable operated Bosch injection pump.  The TDI had more powera drive by wire throttle and injection pump, an intercooler, no cold start assist handle, and the glow plugs were activated by the ignition key.  The 1996 TDI was the first year for the electronically controlled Bosch injection pump. 

The passat TDI was offered in 1996-1997 in the US.  The jetta TDI was offered 1997-1999. Note that some 1999 jetta are actually 4th generation 1999.5 models.  (The 4th generation of VW started in 1998 with the new beetle).  

The only major difference in the mk3 diesels was that some first year 1997 jetta TDI used the 1Z engine from the passat, later years used the AHU engine.  These engines are functionally identical for the average user.  Below are some more differences between the jetta/passat.  Many of their differences are because the passat was available in 1996-1997 and the jetta was available in 1997-early 1999.  Aside from the obvious differences like body panels, size, etc., below is a list of known differences.

Sales numbers for the passat, for North America only
1995: 64 sedans, wagons unknown. (early 1996 models)
1996: 3472 sedans, 1405 wagons.
1997: 2216 sedans, 87 wagons.
1998: unknown. (leftover 1997 models)

Note - for North American market only:  about 2-3 1998 mk4 passats (newer body style) were sold in after use as dealer information and car show demos.  This model was not imported officially because the 90 hp engine was deemed to be underpowered for the newer, heavier passat.  One sedan has been spotted but it had very high wear due to many people getting in and out at car shows, etc.  If you want a mk4 passat, your best option is to get a 2004-2005 passat.  See 1000q: mk3-mk4 generation differences for more details.

Body/Interior

The passat was available in the US as both a sedan and station wagon called the variant, the jetta was available as a sedan only.  The only jetta wagon sold was the mk4 jetta.  Note that many minor panels on the passat station wagon are not compatible with the passat sedan.  For example, the taillights look similar but they have different part numbers!  From the b pillar back, the body panels and interior of the wagon are slightly different.  The headliner, rear seats, rear doors, sheet metal are not interchangeable with the passat sedan.  The wagon and sedan are interchangeable from the b pillar forward.  The station wagon also has a larger fuel tank than the sedan and is the largest fuel tank on any VW diesel sold in North America.  The station wagon can hold about 3 gallons more than the sedan, 8 gallons more if you use the vented fill up capacity.  See 1000q: venting the fuel tank for more details on that.

Although the passat front seats look similar to the jetta, the passat has one more axis for adjustment of the seat.  The front seats can be directly swapped between mk3 cars but cannot be swapped between mk3 and mk4 cars without customization of the brackets.  The offset of the jetta/passat seats are not the same.  If you put jetta seats into the passat, it shifts you towards the door about 3/4 inch so that the steering wheel is slightly to the side, most people don't notice it.

No passat is prewired for cd changers.  Later jetta may be wired for cd changers, some are not.  The passat/jetta cd changers are not compatible with each other because they used a different head unit (radio).  Late jettas had a different head unit that was used with mk4 style cd changers. 

The passat has a interior cabin air filter.  The jetta does not but it can be added, just add a foam gasket and bracket.

Engine

The engines are almost identical with a few small differences, and most of the parts are interchangeable between the 1Z and AHU:

The passat and jetta do not have an anti shudder valve.  All later generation mk4 diesels have an anti shudder valve.  

The 1996 passat has an EGR but no EGR cooler, the 1997 jetta and passat and all tdi models afterwards had both EGR and EGR cooler.  Sending the exhaust gas through a cooler (cooled with engine coolant) before putting it through the EGR valve into the intake reduces nox emissions  No EGR at all can produce three times as much nox as a properly functioning EGR.  Note that in all cars, the EGR valve is shut at full throttle, so the EGR has no effect on top end power.  Because the 1996 model does not have the EGR cooler it is slightly easier to remove the intake manifold for cleaning or repair and has higher nox emissions.  Refer to 1000q: intake removal for details on removing the intake or EGR for cleaning.

The 1996 passat used a supplementary 5th injector for emissions that was removed for 1997 models and should be disabled for less smoke.  See 1000q: 5th injection disable on 1996 passat for more details.  

The engine in the 1996-1997 passat and some 1997 jetta is the 1Z motor.  All other jettas 98-99 use the AHU engine.  They are slightly different but have many interchangeable parts.  The mk3 jetta AHU engine pistons are the same as mk4 jetta ALH and Euro only 110hp AFN engine pistons.  The piston is stronger than the passat and early 1997 1Z pistons.  The head design is also stronger but uses smaller valves.  There is no functional or noticeable difference to the driver.  The only case in which the 1Z's weaker engine would make a difference is if you are custom modifying your power levels way beyond the scope of this article.

For some reason, there was a parts shortage, so a few 1Z engines had undersized pistons.  This could cause a low reading on the compression test due to excess clearance and excessive engine wear.  Read how to do a compression test at 1000q: compression test - how to.  The only solution is an engine rebuild with the correct pistons.

The injection pump in the jetta AHU engine uses a higher pressure with higher break pressures.  The mk3 cars used 4 different part numbers for injection pumps, 3 of which are interchangeable without any problem.  Note that the VW part numbers do NOT reflect the changes in the Bosch part numbers and small changes so the dealer will not know about the differences, I think the VW part number catalog shows the same part number for all mk3 cars.  The big difference was an increases in fuel pressure in the AHU pump.  The 1Z passat used a lower fuel pressure pump partly due to a different cam used in the injection pump.  The AHU used a higher pressure injection pump due to the cam and is plug-play with the 1Z.  See 1000q: renault injection pump disassembly part 1 and disassembly part 2 for a detailed look at a diesel injection pump showing the cam plate inside of an injection pump.  The renault pump is not for the VW but it similar in design to earlier VW injection pumps.  You can also retrofit an injection pump from an mk4 car, see 1000q: ALH injection pump swap for more details.

The jetta uses a KKK-03-06 turbo, except 1997 which may have the 1Z engine.  The 1Z engine (all passat and some jetta), used a Garrett G-15 turbo.  Functionally they are pretty much the same, both are conventional wastegate style turbos, and are interchangeable.  Read more about turbocharging in 1000q: turbocharging.

The jetta has a one way free wheeling pulley on the alternator, the passat does not.

The 1Z and AHU turbo oil line and oil pressure sensor are in different locations.

The original fill coolant on the early passat was blue VW G11 coolant.  The original fill on late passat and all jetta was pink G12.  They are not compatible and should not be mixed.

Other mechanical

The mk3 diesel passat and jetta were available as manual transmission only.  They were available with an automatic transmission with a gasoline engine.

The security system alarm horn is mounted under the driver's side windshield molding in the jetta.  The passat alarm horn is in the passenger side fender well.

The n75 solenoid, the one that controls the turbo wastegate, is on the top driver's side firewall on the passat.  In the jetta, it is by the accordion hose on the passenger side.

The passat has rear disc brakes.  The jetta has rear drum brakes but they can be converted to disc brakes.  Front brakes are identical.

The front suspension lower control arm bushings on the 1990-97 passat, 1985-2005 golf/jetta/newbeetle, 1995-2002 cabrio, 1990-1995 corrado are all the same, you can replace them with Audi TT bushings for a firmer feel, all are interchangeable.  Note that there were 2 versions of the Audi TT bushings, one small and one post-recall larger bushing. 

Due to the additional size and weight of the passat, everything else being equal, it will have less performance/handling/mileage such as braking and acceleration because the front brakes and engine/transmission are almost identical to the jetta.

The 1996 passat has an extra 5th fuel injector that adds fuel to the catalytic converter to improve emissions.  They also may smoke more due to the poor function of this 5th injector.  The fix for this is converting to the 1997 passat ECU that compensates for the lost injector (for emissions) and fuel injectors.

Different ECU between 1996, 1997 passat and jetta.  The 1996 uses a plastic cased BK ecu, the 1996 with the ecu recall uses the metal cased GQ ecu, the 1996 passat uses the metal cased FA ecu.

1996 passat is OBD-I.  1997 passat is OBD-II.  The 1996 with the pre-recall BK ecu has a feature where you can get some check engine codes by turning the key to "on" and pumping the throttle all the way to the floor 5 times in under 5 seconds.  Count the number of blinks of the check engine light (CEL). The four digit code will be displayed as four counts of blink that will repeat ( **,**,**,*....**,**,**,*...). In this example the code is 2221, Manifold Absolute Pressure control.  Note that the blink code is different than the vag-com code (00575).
Blink code 4444 indicates a BK ECU with no faults of those supported. A constantly illuminated CEL, no blink at all, indicates a non-BK ECU. 

Note that the passat 1996 recall GQ ecu and the 1997 FA ecu do not have the code feature.  Since the 1996 recall ecu does not have this feature and it wont' display all of the codes accessible with a VAG-COM, this feature is effectively useless.

Also note that the BK ecu circuit board is not compatible with any other car other than the 1996 passat.  If you need a replacement and don't have a post recall GQ ecu, you can use an A3 Jetta's JB ecu and have the data reflashed to work on your 1996 car.  

The passat has a switch under the clutch pedal that is connected only to the cruise control circuit.  Most cars including the mk3 jetta also has this switch connected to the starting system clutch interlock in addition to the cruise control.  You must press down the clutch pedal to start the jetta but not the passat.

Do you know something that should be added to this article?  Post your comments in the myturbodiesel.com forums

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